There were a whole bunch of cartridge / cassette systems made to record
and play back RS-232 data. Sykes (made the 4912 cassette unit for
Tektronix) , Memodyne, Teac, Sy/MAX and many others made them. I have a
Tektronix 4923 that I've used in line with a 4006 terminal connected to
a PDP-8e. Used to load / save programs etc. A bit awkward to use
sometimes but it's better, and faster, than paper tape. Nice that it's
vintage also. Some of these are incremental tape drive systems and can
record single characters at a time. I had a Plessey recorder that could
do that though it was a 7 bit parallel system.
Bob
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Vintage computers and electronics
www.dvq.com
www.tekmuseum.com
www.decmuseum.org